1. Field of the Invention
The present invention is related to electrical interfaces, more particularly it relates to a multi-protocol electrical interface.
2. Description of the Prior Art
Serial communications, synchronous or asynchronous are typically defined by standards, such as those set by the Electronic Industries Association/Telecommunications Industry Association (EIA/TIA). These standards define interfaces such as, but not limited to, EIA/TIA-232, ELI/TIA-449, EIA/TIA-530, and EIA/TIA-530A, which are also well known in the industry under the former EIA prefix “RS-” (Recommended Standard) as RS-232, RS-449, RS-530, and RS-530A. Additional interfaces include International Telecommunications Industry (ITU) X.21 and V.35. Also, the Institute of Electrical and Electronics Engineers (IEEE) 1284 standard define interfaces for parallel communications. These standards define communication protocols, signal levels, maximum bandwidth, connector pin-out, supported handshaking signals, drive capabilities, and electrical characteristics of the serial or parallel lines for data exchange.
Typically, each serial interface operates either as a data terminal equipment (DTE) or a data circuit-terminating equipment (DCE). Typically, a terminal or computer is referred to as the DTE and a modem is typically referred to as the DCE. A signal that is an output on a DTE is the input to a DCE on the opposite end of the serial interface. Generally, the DTE and the DCE have complementary mechanical connectors, which can be coupled to allow an interchange of binary signals between the electrical interface standards in the industry. With the abundance of interface standards in use it is difficult to design DTEs that will interconnect with the wide range of available DCEs. Most existing DTE interconnection devices only support a single type of interface. In order to perform the data exchange according to the selected protocol it is necessary to establish a number of electrical connectors having predetermined characteristics. Typically this is done by a mechanical connector having a defined configuration of pins, e.g. a RS 232 DB-9 connector with 9 pins or a DB 25 with 25 pins.
Several attempts have been made to develop a DTE interface that will support multiple interface standards.
In other DTEs and DCEs, this problem is solved by having a separate cable for each of the interface standards and by routing the signals, depending upon which standard is being used, to a corresponding receiver or set of receivers. In this example, a common connector is used at the interchange interface and has a group of pins dedicated to signals that are unique to each interface standard. This method, however, requires larger connector space.
Another solution has been to include a number of interface boards in the DTE or DCE, each board corresponding to a particular electrical interface standard. These boards remain available at all times so that they may be switched into and out of the respective DTE or DCE depending upon which electrical interface standard is being implemented at that time. When not in use these boards are left idle or are removed and can be easily lost or damaged.
Therefore, these solutions require additional hardware that can be easily misplaced and needs to be at an arm's length to cater for the different application environments. Also, there is substantial time expended configuring the DTE to the DCE. Some devices use a single connector to accommodate all the different possible industry interfaces; however, this makes for a rather bulky and expensive connector. These proposed solutions are not ideal for portable or handheld computers, where portability, flexibility and a minimum footprint are most desirable. These hand-held computers may be used in harsh environments such as industrial plants where there could be hazardous materials or measurements performed in confined spaces, and the connectors must withstand the physical conditions imposed by these environments. The cost of a ruggedised, large connector is prohibitive.
It is therefore an object of this invention to mitigate or obviate at least one of the above-mentioned disadvantages.